1. Field of the Invention
The present invention relates to a hydraulic control unit, in particular for a folding roof of a vehicle. The invention also relates to a folding roof assembly comprising such a hydraulic control unit, and to a vehicle of the convertible type which is provided with such a folding roof assembly.
2. Description of the Prior Art
A generally known hydraulically operating control unit for a folding roof of a convertible car comprises for each pair of hydraulic double-acting cylinders connected in parallel two electrically operated 3/2 control valves for controlling the movements of said cylinders. This makes it possible to drive the movements of the parts of the folding roof in a simple manner, but has the disadvantage that many relatively expensive electrically operated control valves are necessary, with the result that the cost of this known control unit is undesirably high.
Folding roof assemblies with a less expensive hydraulic control unit are already known from the prior art, for example as described in EP 0 425 156 and EP 0 656 274.
In EP 0 656 274 the present applicant proposes a hydraulic control unit with a reversible pump, in the case of which the suction/delivery ports of the pump are each connected individually to an entry port of a corresponding AND valve, and both suction/delivery ports are connected to a common OR valve. By means of an electrically operable valve, the exit of said OR valve can be selectively connected to the other entry port of the two AND valves. The exit port of the one AND valve is also connected to the first connection of the first pair of hydraulic actuators connected in parallel, and the exit port of the second AND valve is connected to the second connection of said first pair of hydraulic actuators. Although the measures proposed in EP 0 656 274 lead to a reduction in the number of electrically operable control valves, when several actuators are being driven it is found that these measures lead to an even more complex circuit with a considerable number of valves. For example, this emerges from the example described in EP 0 656 274 with reference to FIG. 5, which describes a control unit for driving a standard folding roof assembly with a main bow, a rear bow and a cover, which have to be moved in a likewise standard sequence of movements by corresponding hydraulic cylinders.